Mixers are commonly used throughout the wireless industry to mix a radio frequency (RF) signal with a lower frequency local oscillator (LO) signal to produce an intermediate frequency (IF) signal. Mixers can generally be classified as either narrowband or wideband mixers, with the difference being the breadth of the RF range over which the mixer can operate. Wideband mixers are used across numerous wireless applications and standards, one example of which includes ultra wide-band (UWB) wireless systems.
UWB wireless broadcasts are capable of carrying huge amounts of data up to 250 feet with extremely little transmit power and high immunity to interference and noise. UWB wireless receivers are able to highly resolve signals in multi-path fading channels due to the nature of the short duration transmitting impulse signals. This capability, coupled with the spread spectrum characteristics of UWB wireless systems, make UWB systems desirable for use in a wide variety of high-rate, short- to medium-range communications. The additional ability to locate objects to within one inch attracts military, law-enforcement, and rescue agencies. Other UWB applications include broadband sensing using active sensor networks and collision-avoidance systems.
For instance, the FCC has opened a 3.1-10.6 GHz unlicensed band for UWB communication systems. The power mask within this frequency range is much lower (−41.3 dBm) than other wireless radio channels. Two different approaches to UWB system design have been proposed: (1) single-band impulse radio and (2) multi-band radio. The multi-band approach includes many stringent requirements that challenges the design of the RF frond-end blocks, including frequency synthesizers on both the transmitter and receiver sides, as well as low noise amplifiers (LNAs) and mixers on the receiver side with bandwidths in excess of 500 MHz.
The circuit techniques used to realize different circuit components in a UWB transceiver are typically different from those used in current narrow bandwidth RF technology. This allows the design of new circuit topologies that operate at substantially higher frequencies than conventional circuits, such as distributed circuits. Distributed integrated circuits, such as distributed amplifiers and oscillators, employ actual or artificial monolithic transmission lines, i.e., transmission lines placed directly within the integrated circuit, or “on-chip,” in order to achieve higher frequencies by trading delay for bandwidth.
Delay is more tolerable in wideband systems than in narrowband systems because the delay can be calibrated using the delay prediction circuits. Accordingly, distributed circuit topologies have extended into the design of wideband mixers. These mixers use single-ended architectures fabricated with expensive semiconductor processes such as GaAs and other III-V technologies. These single-ended architectures are prone to failure at ultra high frequencies due to integrated circuit noise. One such design employs a dual gate distributed mixer in high electron mobility transistor (HEMT) technology (see M. Lacon, K. Nakano, G. S. Dow, “A Wide Band Distributed Dual Gate HEMT Mixer,” GaAs IC Symposium Digest, pp. 173-176, 1988). This design uses dual gate transistors to provide the RF and LO signal paths, and thus exhibits a poor return loss.
Another wideband distributed mixer design is fabricated in a Gallium Arsenide (GaAs) pseudomorphic HEMT (PHEMT) technology (see K. L. Deng, H. Wang, “A 3-33 GHz PHEMT MIMIC Distributed Mixer,” IEEE RF Integrated Circuits Symposium, pp. 151-154, 2002). However, this design suffers from a lower conversion gain, high susceptibility to the environmental noise such as inductive noise from the package and power/ground bounce, and high power consumption. Most importantly, the mixer operation is achieved under a precisely equal LO and RF amplitude, which is a severe limitation of the proposed circuit.
Accordingly, improved mixer designs capable of ultra wideband operation with improved conversion gain, lowered noise susceptibility and power consumption, relaxed input signal requirements, lowered fabrication costs and other such advantages are needed.